FIG. 8 shows a system based on the conventional technology disclosed in a U.S. Pat. No. 4,430,864, which is comprised by: process air passage A; regeneration air passage B; two desiccant beds 103A, 103B; a heat pump 200 for regeneration of desiccant and cooling of process air. The heat pump 200 uses heat exchangers 220, 210 embedded in the desiccant beds 103A, 103B as high and low temperature heat sources respectively, in which one desiccant bed performs dehumidifying by passing process air, and the other desiccant bed performs regeneration of desiccant beds by passing regeneration air. After air conditioning is carried out for a specific time interval, four-way switching valves 105, 106 are operated to perform reverse processes in respective desiccant beds by flowing regeneration air and process air in the opposite desiccant beds.
In the conventional technology described above, high/low heat source of the heat pump 200 and each desiccant are integrated in each unit, and, an amount of heat equivalent to the cooling effect .DELTA.Q, is totally loaded on the heat pump (vapor compression cycle). That is, cooling effect cannot exceed the capability of the heat pump (vapor compression cycle) used. Therefore, there is no benefit resulting from making the system complex.
Therefore, to resolve such problems, it is possible to consider a system, such as the one shown in FIG. 9, to heat the regeneration air by placing a high temperature source 220 in the regeneration air passage B, and placing a low temperature air source 240 in the process air passage A to cool the process air, as well as to provide a heat exchanger 104 for exchanging sensible heat between the post-desiccant process air and pre-desiccant regeneration air. In this case, the desiccant 103 uses a desiccant wheel which rotates so as to straddle the process air passage A and the regeneration air passage B.
This system can provide cooling effects (.DELTA.Q), which is a sum of the cooling effects produced by the heat pump and the cooling effects produced by sensible heat exchange performed between process air and regeneration air, as shown in the psychrometric chart presented in FIG. 10, thus producing a system of a more compact design and capable of generating a higher cooling effects than that produced by the system shown in FIG. 8.
In such a heat pump, it is necessary to provide a high-temperature heat source with a temperature of over 65.degree. C. for desiccant regeneration, and a low-temperature heat source with a temperature of about 10.degree. C. for cooling process air. A vapor compression type cooling process for a refrigerant HFC134a is shown in a Mollier diagram shown in FIG. 11. As shown in FIG. 11, the width of temperature rise is 55.degree. C., and the pressure ratio and compressor power are closer to the heat pump in conventional air conditioning system based on refrigerant HCFC22. Therefore, there is a possibility of constructing a heat pump using a compressor for HCFC22 for desiccant regeneration in air conditioning systems, and if the sensible heat in the superheated vapor at the compressor exit (80.degree. C. in FIG. 11) can be utilized, there is a possibility that the regeneration air can be heated to a temperature higher than the condensation temperature.
In a system of such a configuration, when the total volume of the regeneration air is subjected to heat exchange by the high-temperature source heat exchanger of the heat pump, the relation between temperature change and enthalpy for the refrigerant and regeneration air is as shown in FIG. 12. As shown in FIG. 12, if the temperature fraction at the condensation heat conduction region, where the refrigerant of the high-temperature heat source 220 of the heat exchanger is condensed, is taken as 80%, regeneration air can be heated from 40.degree. C. to about 60.degree. C., but the amount of heat that can be supplied by the super-heated vapor of the refrigerant in the overall capability of the heat pump side of the system is only about 12% of the total heat generated, as shown in FIG. 11. For this reason, heating of regeneration air by the 12% contribution is: EQU (20.degree. C/0.88).times.0.12=2.7.degree. C.,
so that sensible heat from the super-heated vapor exiting from the compressor hardly contributes to raising of regeneration air, resulting that it is necessary to regenerate the desiccant material at a temperature (62.7.degree. C. in the figure) lower than the condensation temperature.
On the other hand, when using a material such as silica gel for a desiccant material, the higher the desiccant regeneration temperature up to about 90.degree. C., moisture adsorption capability is higher, therefore, the higher the temperature of the regeneration air, latent heat processing capability of the desiccant-assisted air conditioning system is higher and cooling effects are improved. Therefore, to achieve this end objective, if the condensation temperature is increased to about 75.degree. C. in an effort to increase the regeneration temperature, in the resulting process, the condensation pressure of the refrigerant becomes abnormally high (24.1 kg/cm.sup.2) as shown by the dotted line in FIG. 11, and it is no longer possible to use HCFC22 compressor in designing a heat pump for use in a desiccant air conditioning system. The compressor power is also increased and the performance factor drops.
This invention has been made to provide an air conditioning system that enables to raise the temperature of superheated vapor of the compressed refrigerant in the heat pump, that is, to increase its enthalpy, so as to increase the proportion of sensible heat in an output heat from the high temperature heat source of the heat pump, for heating the regeneration air so as to increase dehumidifying capability of the desiccant. Such a system has a superior dehumidifying capability and produces energy saving, and by obtaining heat sources for regenerating the desiccant from both process air and regeneration air, the desiccant can be regenerated separately before starting the system, and when the sensible heat is small, the system can be operated chiefly through dehumidifying the process air.
This invention has been made in view of the problems described, and the object is to provide a system and a method of operating the system, in which adsorption of moisture by a desiccant and desiccant regeneration to remove adsorbed moisture by a heat pump are performed continually, and the refrigerant flowing in the heat pump is heated by post-desiccant regeneration air to raise the temperature of super-heated vapor, i.e., its enthalpy of compressed refrigerant, thereby increasing the proportion of sensible heat output from the high temperature source of the heat pump before allowing heat exchange to take place with the regeneration air to increase the regeneration temperature of desiccant, thereby increasing the dehumidifying capability of the desiccant. Another object of the invention is to provide an air conditioning system in which, by providing the low-temperature heat source heat exchanger of the heat pump for both process air and regeneration air, and by switching the flow direction of the refrigerant flowing into the compressor, heat source can be obtained for both process air and regeneration air so that regeneration of desiccant can be performed separately before starting the system, and further, when the sensible load is small, the system can be operated based primarily on dehumidifying the process air, thus to provide an air conditioning system having a superior dehumidifying capability and performance characteristics as well as flexible in meeting the requirements of the air conditioning system, and resulting in energy saving.